X-Message-Number: 1993
Date: Fri, 19 Mar 93 13:13:00 CST
From: Brian Wowk <>
Subject: CRYONICS Cold Storage

Ralph Merke:
 
> It would be useful to separate out two issues:
>
> (1) The benefits to be derived from a new design that stores more
> patients, achieving economies of scale
> and
> (2) The benefits to be derived from adopting a higher storage temperature.
 
        I suggest that the following issues can be independently 
discussed as they relate to economies of scale:
 
(1)     Foam vs. vacuum insulation.
 
(2)     -196'C liquid nitrogen (LN2) storage vs. -130'C vapor storage.
 
        Regarding issue (1), the problem with vacuum dewars is 
catastrophic failure.  The bigger the dewar, the bigger the catastrophe.  
Some might say that it's unfair for me to compare the economics of a 20 
person foam-insulated room to 4 person dewars.  But do we really want to 
store 20 patients in a single dewar?  Maybe we would if we had a 100 
patients, but then that raises the question of a 100 person foam-
insulated room....
 
        I am not going to belabor this issue since the answer seems 
obvious.  The best economies of scale will be achieved by storing 
patients in a single large enclosure, and single large enclosures *must* 
be insulated with foam, not vacuum.
 
        One final point is that the manufacture of high-vacuum cryogenic 
dewars is difficult and specialized work done by only three (I think) 
firms in the U.S.  None of them makes dewars suitable for whole-body 
cryonics patients as a stock item.  Thus Alcor's dewars have to be 
special ordered and custom made.  Because of the controversial nature of 
cryonics, only *one* of these firms is still making dewars for cryonics, 
and we don't know for how long.  This state of affairs is absolutely 
unacceptable and in itself is reason enough to go to foam. 
 
        Issue (2) is more complex.  Strictly from the physics point of 
view, -130'C is cheaper storage than -196'C storage.  The temperature 
difference implies that cooling costs will be 44% greater for -196'C 
than for -130'C.  What about capital cost differences?  Having agreed (I 
hope) that foam is the way to go for economies of scale, we are 
essentially comparing a foam-insulated wooden room (-130'C system) with 
a foam-insulated cluster of LN2 tanks (-196'C system).  (You have to use 
a cluster of tanks instead of a single tank so that you can fix leaks.)  
While the cryosuits, thermostats, and air circulators in the -130'C 
system will be expensive, this may be more than made up for by the 
expense of multiple large tanks in the LN2 system.  The LN2 system will 
also weigh hundreds of tons, and probably have to be put below ground.
 
        I seems to me that -130'C vapor storage is at least competitive 
with LN2 storage.  Moreover, the 44% cooling cost difference virtually 
guarantees that at a large enough patient load (20? 50? 100?) -130'C 
will be cheaper than LN2.  I have also been arguing that vapor storage 
done right can be just as reliable as LN2.  Finally, you will notice 
that I have not even mentioned the minor detail that LN2 cracks patients 
into pieces while -130'C does not!    
 
                                                --- Brian Wowk

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